The microcontroller is a semiconductor integrated circuit which is incorporated in equipments such as home electric appliances, AV equipments, mobile phones, automobiles and industrial machines and carries out processing in accordance with the programs stored in memories to control the respective equipments.
Since a failure of a control unit in an automobile may lead to an accident, components including the microcontroller are required to have high reliability and are designed to perform a safety function when a failure occurs so as to prevent a dangerous situation of the automobile by detecting the failure.
The microcontroller is required not only to check sensors and actuators to detect the failure thereof but also to detect a failure of the microcontroller itself.
There are various methods for detecting a failure of the microcontroller, and a method in which CPU is duplicated to cause them to carry out the same processing and the values of buses are always compared is often used. This is the method in which a master CPU and a CPU for comparison carry out the same processing at the same time, and the results thereof are compared by a comparison circuit.
Japanese Patent Application Laid-Open Publication No. 10-261762 (Patent Document 1) discloses a method in which two memories and two CPUs are provided and input/output signals of the CPUs are mutually compared.